1. Field of the Invention
The present invention relates to an optical communication module capable of transmitting an optical signal through an optical fiber. In particular, it relates to an optical communication module which can be utilized for domestic communication, electronics-to-electronics communication, LAN (Local Area Network) and the like by using a multimode optical fiber such as a plastic optical fiber as a transmission medium.
2. Description of Related Art
In the field of an optical communication module for transmitting optical signals using an optical fiber as a transmission medium, an LED has been utilized as a light source for low-speed communication generally for indoor use running at a transmission speed of 100 Mbps or lower. For high-speed communication mostly for major lines running at a speed of Gbps order, an LD (semiconductor laser) has been used as a light source.
In the case of using the LD, though it is not so problematic in using the LED, a light beam emitted from the LD is leaked out of the module when a connector of the optical fiber is detached and the leaked light beam may possibly damage an eye and skin due to coherence thereof. Therefore, use of the LD is strictly regulated by JIS or the like. Accordingly, to restrict the emitted light beam within the module even if the connector is detached, various ideas have been made, such as (1) mechanically preventing the leakage of the light beam emitted from the LD by providing a shutter and (2) sensing the removal of the connector to electrically turn off the LD.
Japanese Unexamined Patent Application No. Hei 9 (1997)-211264 discloses an example of the above idea (1). This will be described below with reference to FIGS. 17 and 18.
FIGS. 17 and 18 show a shutter 101 for preventing the leakage of a transmission light beam, which is a fundamental constituent of the invention, an emitting member 102 for emitting a transmission light beam, a receptacle 103, a cylinder 104 for fixing a ferrule, a connector 105 of an optical fiber, a ferrule 106, and a transmission light beam 107 to be coupled with an optical fiber 108.
The shutter 101 is formed of an elastic material such as phosphor bronze. As shown in FIG. 18, when the connector 105 is attached, the shutter 101 is pushed down to open by the optical fiber 108 without inhibiting the insertion of the optical fiber. The transmission light beam 107 is coupled with the optical fiber 108 enclosed by the ferrule 106.
When the connector 105 is detached, the shutter 101 returns to its original position by spring force and blocks an optical path of the transmission light beam. Thus, the transmission light beam is prevented from emitting to the outside of the module.
In recent years, high-speed communication at several hundred Mbps is required even for indoor electronics-to-electronics communication in the home due to the spread of IEEE 1394 and ATM. According to this, the LD is becoming more popular than the LED as the light source. In this case, the attaching/detaching of the connector is repeated many times incomparably to the cases of the major lines and the interoffice LAN. The above-described conventional technique utilizing the mechanical means for preventing the light leakage becomes unreliable when the connector is repetitively attached/detached. Further, in view of production costs, it is not preferable to provide a shutter or the like in a fine optical communication module.
The method of electrically sensing the removal of the connector may be more reliable than the above-described mechanical method. However, it has no 100% guarantee of reliability and is unpreferable in view of fail-safe, a fundamental idea for the safety of human body. Further, the method also requires considerable costs.
Alternatively, it may be possible to constantly decrease the output of the LD. However, an amount of the transmission light beam coupled with the optical fiber is reduced, which decreases the SN rate and hinders long-distance transmission.